The dye waste stream from plants that make or use dyes generally contains many different colored residues which do not undergo rapid biodegradation. The use of reducing agents such as sodium hydrosulfite (also called sodium dithionite), formamidine sulfinic acid (FAS) , and sodium borohydride to decolorize dye manufacturing and textile dyeing effluents have been described in the literature. Simple reduction by these agents results in a yellow colloidal solution. Some examples of references discussing this technology include: M. Kolb et al, Melliand Testilber 1988, 69(4), E155.286-7: Chem. Abstr. 1988, 108: 2262993h; A. Reife Book Pap.--Int. Conf. Exhib. AATCC 1990, 201-4: Chem. Abstr. 1991, 114: 149417w; and D. L. Michelson et al, "Chemical Pretreatment of Concentrated Reactive Dye Discharges Prior to Biodegradation", presented at Amer. Chem. Soc. Emerg. Techn. for Hazardous Waste Management, Oct. 3, 1991 (and references therein).
Other references which discuss this problem and/or possible solutions include: H. Takahashi and T. Fujii, Japanese Kikai Tokkyo Koho, 79: 29,897, Mar. 6, 1979, Chem. Abstr. 1979, 91.44165r; Y. Tanto et al, Japanese. Kikai Tokkyo Koho, 77: 116,644, Sep. 30, 1977, Chem. Abstr. 1978, 89: 30358c; R. Tanaka et al, Seni Kako 1976, 28(1): 14-19, Chem. Abstr. 1976, 85: 112355f; D. Kupfer, German Offenlegenschrift 2323600, Nov. 21, 1974, Chem. Abstr. 1975, 82: 89847v; M. Sarvwatari, Senshoku Kenkvu 1980, 24(4): 142, Chem. Abstr. 1981, 95: 224973u; and Ml Kaimori et al, Japanese Kikai Tokkyo Koho, 63: 69,589 (88 69,589) Mar. 29, 1988, Chem. Abstr. 1988, 108: 226364g. However, simple treatment with hydrosulfite does not produce a water suitable for reuse in dyeing.
An improved method of treatment employing sodium bisulfite catalyzed sodium borohydride with a cationic agent has been reported by Cook, et al in U.S. Pat. No. 4,975,203. Another improved method of treatment employing flocculation with a cationic polymer followed by treatment with a reducing agent such as sodium hydrosulfite has been patented in U.S. Pat. No. 5,360,551 by Weber.
Other additives have also been tried to remove impurities from such systems. The use of aluminum salts to treat waste water has a long history. Alum has been one of the most effective coagulants used. (See Kirk Othmer, (3rd edition Vol.2 (1978), at pages 244ff and Vol. 24 (1984) at pages 295ff). More recently, other aluminum salts that are more basic such as polyaluminum chloride and polyaluminum chloride sulfate have been used and have been found more effective in waste treatment than alum. Aluminum hydroxychloride, an 83% basic material containing 23% aluminum as alumina has only recently found application in the waste treatment industry.
There have been problems with all of these efforts, however. One problem is that large volumes of solids are produced. Another is that the floc produced settles slowly, if at all, and finally, the effluent from some types of treatments still retains a yellow color resulting in staining of the cloth when the water is reused in dyeing. The need to recycle makes the yellow color undesirable or unacceptable while the large volumes of solids produced create their own disposal problems and slow settling solids create the need to have very large and expensive settling basins.
In addition, these previous attempts at treating such effluents still leaves dissolved salts in the water. High concentration of dissolved salts in effluent present problems in treating the textile plant effluent and the receiving waters. Usually these salts are discarded with the dye waste to a lagoon or sewer system. The ability to reuse such water in the manufacturing process would be a valuable benefit from a cost and environmental viewpoint.
Thus, there still remains a need for improved processes for decolorizing effluent containing dyes. Therefore, it is an object of this invention to provide a method for decolorizing textile waste water or other types of effluent containing color materials which results in a less colored effluent and at the same time produces a compact and rapid settling floc. It is another object of this invention to provide a method for decolorizing such water in a way which allows effluent to be recycled into the manufacturing process. These and further objects of the invention will be apparent from the following description.